1. Field of the Invention
The present patent application for industrial invention relates to a drilling machine or drill provided with an optimized tool unloading system.
2. Description of Related Art Including Information Disclosed Under 37 CFR 1.97 and 37 CFR 1.98.
FIG. 1 shows a drilling machine, which is generally indicated with reference numeral (100). The drilling machine (100) comprises a drilling tool (U) used to drill holes into the ground. When the machine is operated, the tool (U) is driven into the ground to drill the hole. Afterwards, the tool (U) is extracted from the ground and unloaded, ejecting the soil that adheres to the tool. Unloading is obtained using the centrifugal force, by increasing the speed of rotation of the tool, and/or using the force of inertia, by stopping the tool suddenly in such way to remove the soil from the tool.
The drilling tool (U) is connected to a telescopic drilling bar, which is generally known as kelly bar (K).
The tool (U) is actuated by an actuation unit, which is generally known as rotary (R). The rotary (R) comprise a gear transmission composed of one or more pinions that engage in a toothed wheel fixed to the tool (U). The rotary (R) is mounted on a mobile support (101) in such manner to place the rotary in position and drive the tool into the ground.
As shown in FIG. 1A, the drilling machine (100) transmits the torque to the tool (U) by means of a kinematic chain composed of a hydraulic motor (M) with large size, generally with variable cylinder capacity, coupled with a speed gearbox (C) that in turns transmits motion to the toothed crown of the rotary (R). Although FIG. 1A shows two hydraulic motors (M) and two gearboxes (C) provided with output pinions that engage in the toothed wheel of the rotary (R), the following description will refer to one hydraulic motor and one gearbox, it being understood that the drill (100) can be provided with multiple hydraulic motors and multiple gearboxes.
The hydraulic motor is fed by a pump actuated by the main motor, generally an internal combustion engine, such a diesel engine.
The speed gearbox (C) is a device that contains at least one epicycloidal reduction gear and at least one clutch. As shown in FIG. 2, each epicycloidal reduction gear (2) comprises an input shaft (20) connected to the drive shaft of the hydraulic motor (M).
The input shaft (20) is connected to a planetary gear (21) that supports satellite gears (22) engaging on the external toothing of an output pinion (23) and on the internal toothing of a peripheral toothed wheel (24), which is known as fixed wheel. The output pinion (23) engages in the toothed wheel of the rotary (R).
The drive ratio of the motion of the epicycloidal reduction gear (2) is given by the Willis equation:
      τ    0    =            ω2      -              ω        ⁢                                  ⁢        p                    ω1      -              ω        ⁢                                  ⁢        p            
wherein ωp is the angular speed of the input shaft (20) connected to the planetary gear, ω1 is the angular speed of the output pinion (23) that engages in the toothed crown of the rotary and ω2 is the angular speed of the peripheral toothed wheel (24).
By sending a pressure signal to the gearbox (C), the clutch of the gearbox (C) either blocks or unblocks the peripheral toothed wheel (24) of the epicycloidal gear, changing the drive ratio between the input shaft (20) and the output pinion (23) and consequently the speed of rotation of the tool (U). In practical terms, when the gearbox (C) is hydraulically actuated, the drive ratio is 1:1, whereas when the gearbox (C) is not actuated, the ratio is higher, generally 1:4, 1:5 or 1:6.
In some instances an auxiliary hydraulic motor (not shown in the figures) is used instead of the gearbox (C) to unload the tool (U), said auxiliary motor having a fixed cylinder capacity and dimensions lower than the hydraulic motor (M). During the unloading operation the hydraulic motor (M) is disconnected and the auxiliary motor is activated. The hydraulic motor (M) is powered by one or more pumps with variable cylinder capacity that adjust their cylinder capacity according to the load and other parameters. The pumps are powered by the diesel engine.
During the drilling operation the variable cylinder capacity of the hydraulic motor (M) allows for changing the speed of the tool (U) (regardless of the gearbox (C)) according to the ground conditions. However, during the drilling operation, it is better to operate the tool at constant speed, without changing the cylinder capacity of the hydraulic motor.
Hydraulic motors that progressively change their cylinder capacity according to the pressure on the motor are known. However, this type of hydraulic motors are not used for drilling machines because during the drilling operation it is better to operate with a constant speed and accordingly with a constant cylinder capacity.
In the following description, the term “minimum cylinder capacity” is the minimum cylinder capacity that can be physically reached by the motor without breaking down; the term “maximum cylinder capacity” is the maximum cylinder capacity that can be geometrically reached by the motor; the term “low cylinder capacity” is a cylinder capacity comprised between 20% and 40% of the maximum cylinder capacity; and the term “high cylinder capacity” is a cylinder capacity comprised between 80% and 100% of the maximum cylinder capacity.
It must be considered that the torque of the hydraulic motor is in direct relation to the cylinder capacity and is defined by the following formula:
  Torque  =                    Cylinder        ⁢                                  ⁢        capacity        *        Δ        ⁢                                  ⁢        P        *        η                    20        *        π              *    k    ⁢                  ⁢    1  
wherein ΔP is the difference in pressure between upstream (input) and downstream (output) of the hydraulic motor, η is the output of the hydraulic motor and k1 is a proportionality constant.
On the contrary the speed of the output shaft of the hydraulic motor is in inverse relation to the cylinder capacity and is defined by the following formula:
  Speed  =            (                        1000          *          Capacity          *          η                          Cylinder          ⁢                                          ⁢          capacity                    )        ⁢                           *            ⁢      k        ⁢                  ⁢    2  
wherein k2 is a proportionality constant and the capacity is given by the following formula:
  Capacity  =            Power              Δ        ⁢                                  ⁢        P              *    k    ⁢                  ⁢    3  
In general, in order to work on very hard ground, most drills change the cylinder capacity of the hydraulic motor (M) in such manner to operate it with high cylinder capacity and have a higher torque to drill the ground.
Instead, drills of different manufacturers differ in the operation during the unloading of the tool.
It must be noted that, in case of medium-sized machines, the mass of the kelly bar (K) and the tool (U) filled with soil can reach 11,000-12,000 kg.
Until today the unloading of the tool in drilling machines is made in the following ways:                only by means of the centrifugal force (by turning the tool rapidly, the centrifugal force tends to remove the soil excavated by the tool) or        by means of the centrifugal force and the force of inertia obtained by stopping the tool suddenly.        
The machines that operate by means of the centrifugal force can work in two different ways:                setting the hydraulic motor (M) at the minimum cylinder capacity to obtain the maximum speed of the tool (U) without overrunning the gearbox (C); or        disconnecting the main hydraulic motor and connecting the auxiliary hydraulic motor that, having a small cylinder capacity, guarantees a high speed of rotation of the tool. In such a case, the overrunning of the gearbox (C) is avoided because the gearbox (C) is by-passed and the auxiliary hydraulic motor is provided with its own reduction gear with a low drive ratio, which therefore can withstand high input speeds.        
On the contrary, in the machines that unload the tool by means of the centrifugal force and the force of inertia, the tool is operated at a high speed of rotation and is stopped, inverting the direction of rotation and repeating this operation several times. Generally, this is the operation mode of the machines with gearbox (C).
However, in both cases the cylinder capacity of the main hydraulic motor (M) or the auxiliary hydraulic motor is fixed during the unloading operation. As a matter of fact, the cylinder capacity of the main hydraulic motor (M) is fixed by the manufacturer of the drilling machine at a minimum value that prevents the overrunning of the gearbox (C). Instead, the auxiliary motor has a fixed (not variable) cylinder capacity that is chosen by the machine manufacturer.
When a motor with fixed cylinder capacity is used during the unloading of the tool, the load on the machine pumps is quite high, having to accelerate a very large mass. Therefore, for a few seconds, the hydraulic system must operate at the maximum pressure, meaning that oil is discharged through a safety valve of the hydraulic system, which is known as pressure relief valve. This causes the overheating of the hydraulic fluid in the hydraulic system, which is considerably heated also during drilling, when the machine generally works at pressure values close to the maximum pressure.
Consequently, the unloading of the tool risks heating the oil further, instead of cooling it down. The temperature increase of the fluid in the hydraulic system impairs the performance of the machine. As a matter of fact, when a certain temperature is reached, the machine computer will reduce the power of the diesel engine to protect the pumps, the gaskets and the other parts of the hydraulic system.
In addition to the overheating of the hydraulic system, also the performance of the drilling machines of known type is impaired. As a matter of fact, it is difficult to accelerate a mass of 11,000-12,000 kg with an engine that works at the minimum cylinder capacity with a low torque. The performance of the machines provided with gearbox (C) in which the tool is unloaded by means of the force of inertia and the centrifugal force can be so modest to induce the operator not to operate the machine with the gear having the lowest gear ratio.
In the drilling machines provided with gearbox, such an inconvenience may be partially solved if during the unloading of the tool, the operator starts the unloading operation with a low gear and gradually uses higher gears in order to increase the speed. However, it must be considered that gear changing is not an easy operation in drilling machines and the operator generally performs the entire unloading operation with the same gear, which is empirically chosen according to the user's experience.
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The purpose of the present invention is to eliminate the drawbacks of the prior art by devising a drilling machine that is efficient, effective and reliable during the unloading phase of the tool.